Line scanner for infrared radiation

ABSTRACT

A line scanner for infrared radiation includes a rotatable unit which houses two optical systems, each responsive to different ranges of wavelength. A deflector arrangement deflects the optical axes of these systems in two directions along the axis of rotation of the unit. The first optical system is connected to an infrared detector whereas the second system is used for orientation purposes either by (1) forming a visible image of the field to be scanned or (2) emitting light pulses in a predetermined direction for reference.

United fttat l l I UN Inventor Claes Thomas Ohman wsqeg fgwre FORMISSlNG XR Filed Nov. 19, I969 Patented July 20, i971 Assignec AGAAktiebolog Lidingo, Sweden Priority Nov. 29, 1968 Sweden [6280/69 LINESCANNER FOR INFRARED RADIATION 13 Claims, 3 Drawing Figs.

U.S. CI...L 250/833, 250/234, 250/236 Int. Cl H01] 3/14 Fieldolsearch..250/83.3 H,

References Cited UNITED STATES PATENTS 2,968,735 l/l96l Kaufold et al.250/236 X 3.200,0l0 ll/l965 Hand, Jr. 250/833 H 3,237,010 2/I966 Elliottet al. .t 250/833 H Primary Examiner-Archie R. Borchclt A!torney-Larsonand Taylor ABSTRACT: miner for infrared radiation includes a tee etam iYXI3IhIl9PLYLQBP RfiE T each responsive to different ranges of waveleiigthfx deflector arrangement deflects the optical axes of these systems intwo directions along the axis of rotation of the unit. The first opticalsystem is connected to an infrared detector whereas the second system isused for orientation purposes either by (l) forming a visible image ofthe field to be scanned or (2) emitting light pulses in a predetermineddirection for reference.

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INVENTOR CLAES THOMAS GHMAN' BY. A d

LINE SCANNER FOR INFRARED RADIATION FIELD OF THE INVENTION The presentinvention relates to line scanners for infrared radiation. "I,

BACKGROUND OF THE INVENTION Line scanncrsgencrally include anoscillating or rotating element which is used for producing therequisite scanning movement and for causing a right-angle deflection ofthe optical axis of the scanner whereby infrared light received by thescanner is directed toward an infrared detector. It is, of course, veryimportant that the field of scan be referenced so that the detectedsignal can be correlated with the scanning movement.

SUMMARY OF THE INVENTION It will be appreciated from the discussionhereinabove that in many instances it will be of advantage to provide asecond optical system, which may be responsive to visible light or toanother range of infrared wavelengths, for purposes of orientation.Where the second optical system is responsive to visible light, thesystem may form an image of the scanning field for orientation. It isnoted that an infrarcd-responsivc optical system is generally notsuitable for forming an image of the scanning field in that the responseof such a system to visible light will tend to be too low. In anotherapproach, the second optical system may be used for transmitting a lightpulse used in orientation.

In accordance with a presently preferred embodiment ofthe invention aline sgan ner is providedyvhioh i ncludes a rotatable ynitincludTrTgTfirst anidfsecond optical All eflecting that controlledrotation of the unit through a predetermined angle will causepositioning of the infrared detector such that the response of thedetector to a particular selected area of the scanned field can bedetermined. For example, where the axes of the two optical systems arespaced-apart by 180', the unit can be turned manually until the desiredpoint appears in the image field. Then by rotating the unit through anangle of I80" the detector will provide an indication of the infraredresponse in the selected direction.

In a second embodiment the optical reference means may comprise a lightpulse generator for producing synchronous light flashes to provideorientation of the detected infrared radiation relative to the scannedfield.

Other features and advantages of the present invention will be set forthin or apparent from the detailed description of preferred embodimentsthereof found hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic sectional viewof a scanning unit in accordance with one embodiment ofthe presentinvention;

FIG. 2 is a sectional view taken generally along the line ll-ll in FIG.I and further illustrates a device for producing control pulses; and

FIG. 3 is a schematic circuit diagram of the electrical circuitryutilized in accordance with one embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. I, aschematic representation of a line scanner in accordance with thepresent invention is shown. The scanner includes a housing includinginternal bearings 12 for rotatably mounting a scanning unit I4.Rotatable unit 14 includes first and second optical systems 16 and I8.Optical system I6 responds to infrared light and collects or receivesradiation directed along the optical axis thereof, this axis beingdenoted 16a. Infrared light received by optical system I6 is reflectedfrom a mirror surface provided on a deflector device 20 in the form ofaprism. The infrared light is deflected from prism 20 along the axis ofrotation [4a of unit 14 and is passed through a collimating lens 22 anda filter 24 to a positive lens 26 which focuses the light onto adetector 28. Filter 24 and detector 28 together determine the range ofinfrared wavelengths to which the instrument responds.

The optical axis 180 of the second optical system 18 is colinear withoptical axis 160 of the first optical system 16. The second opticalsystem 18 may respond to a different range of infrared wavelengths thanoptical system I6 but in the embodiment under consideration, opticalsystem I8 responds to visible light. Optical system 18 directs receivedlight toward the undersurface of the mirror surface of prism 20, thelight then being reflected along the axis of rotation 14a of unit 14 asabove. The light reflected from prism 20 passes through a lens 30 and adeflecting prism 32 to a signal device 34. Signal device 34 is used inproviding orientation of the infrared light received by detector 28 and,as discussed hereinabove, may take either of two general forms. In oneembodiment of the invention, signal device 34 may comprise animage-viewing system such as an eyepiece. In a second embodiment, thesignal device 34 may take the form of a light ulse generator foremitting a flash of light used to indicate a selected referencedirection within the scanning field. In both embodiments a motor 36 maybe utilized to provide rotation of unit 14, motor 36 being coupled tounit I4 through a gearing arrangement denoted 38.

Considering the embodiment of the .invention wherein signal device 34comprises an image-viewing system such as a lens, the radiation from aparticular direction can he found by disconnecting. motor 26 and turningthe rotary unit I4 manually until the desired point or area of interestappears in the image field of the viewing system. As can be best seen inFIG. 2, axes I60 and 18a are spaced-apart angularly by 180 and thus whenunit 14 is rotated through l detector 28 will be responding to infraredradiation from the particular point or area in question in the scanningfield. The motor 36 can be utilized to provide precise rotation of unit14 through the desired angle although this operation can also beperformed manually.

As discussed hcreinabove, signal device 34 may also be used to producesynchronous light flashes to indicate a predetermined referencedirection within the scanning field. For such an embodiment, motor 36 isutilized to rotate unit I4 at a constant speed such as, for example,rpm.

Referring to FIG. 2, an arrangement including a contact control cam 40is utilized to create synchronous control pulses. These pulses may beused in directly producing the synchronous light flashes referred tohercinabove although, in the embodiment underconsideration, thearrangement shown in FIG. 2 is used in providing control pulses denotedA and B for the electrical circuit shown in FIG. 3. For this embodimentthe unit 14 is driven at a constant speed by motor 36 and signal device34 comprises a light-pulse generator for transmitting synchronousflashes of light through the second opti: cal system I8. Referring toFIG. 2 again, the pulse A is ofa duration corresponding to the durationof the infrared scan. Pulsea A and B are out of phase and thus if lightpulses are transmitted responsive to pulse 8 when the second opticalsystem is oriented in a predetermined direction relative to the scanningfield, then the first optical system 16 will be oriented in the samedirection during the rotation of unit 14 at a time bearing thecorresponding relationship to pulse A.

Pulses A and B may be generated in any known manner and in FIG. 2 arotating cam disc 42 is utilized to provide selective opening andclosing of first and second switch contacts 43a and 43b. Cam disc 42 isdriven in synchronism with rotatable unit 14 and includes an outwardextending cam portion 42a of an angular extent corresponding to theangular extent of the scanning field. For example, where scanning isprovided during one-fourth of the period of rotation of unit 14, thebeginning and end of the cam portion 42a of cam disc 42 will beseparated by 90. As stated, the cam portion 42a of cam 42 controlsactuation of contacts 430 and 43b which are disposed in diametricalopposition to one another about the periphery of cam disc 42 so as tocreate pulses A and B discussed hcreinabove.

Referring to FIG. 3, the electrical circuit diagram for the systemreferred to hereinabove is shown. An image display tube 44 includeshorizontal and vertical deflection systems 46 and 48 and an image screen50 used in displaying the variation intensity of infrared radiationalong the line of scan. A plot of the infrared radiation intensity as afunction of the scanning position is indicated as graph F. The imagescreen 50 is also used to display a marking pulse E" used in indicatingthe position of the light pulses produced by signal device 34 relativeto the scan field.

The control circuit of FIG. 3 includes first and second input terminals560 and 56b which are connected to receive pulses A and B, respectively.Terminals 56a and 56b are connected to the inputs of an OR-circuit 58,the output of OR-circuit 58 being utilized to control a sweep generator60. Thus sweep generator 60 generates a pair of sawtooth pulses Ccorresponding to, and in coincidence with, pulses A and 8 during eachrotation of unit 14.

Terminal 56b is also connected to a first input of an AND- circuit 62.The output from sweep generator 60 is also applied to one input of avoltage comparator 64 which is connected through a differentiating andclipping circuit 68 to the second input of AND-circuit 62. The secondinput to voltage comparator 64 is connected to the sliding contact ofapotentiometcr 66. Voltage comparator 64 compares the amplitude of thesweep voltage produced by sweep generator 60 with the reference voltageprovided by potentiometer 66 and produces an output D in the form ofpulses of variable duration, as indicated. The differentiating andclipping circuit 68 differentiates the output D from voltage comparator64 and suppresses the negative spikes created from the rear flanks ofthe pulses to thus produce a marking pulse E. The position of themarking pulse E along the line of scan corresponds to the time at whicha sawtooth pulse produced by sweep generator 60 reaches the referencevoltage level provided by potentiometer 66. With a reference pulse Bapplied to one input thereof and marking pulse E applied to the otherinput thereof, AND-cirsuit 62 will produce an output for every secondmarking pulse as indicated. This output is utilized to energize a lightpulse generator 70 and is also connected to a first input terminal of atwo-position switch 72. Switch '72 is synchronously operated such thatthe switch contact will be in the upper position denoted B during thetime corresponding to pulse B and in the lower position denoted A duringthe time corresponding to the duration of pulse A. During the timecorresponding to the duration of pulse B the marking pulse E is appliedto dis play tube 44 and the graphical representation thereof, denoted E"and referred to hereinabove, appears on screen 50. Marking pulse E thusindicates the time during the scan at which the light pulse generator 70is actuated.

Considering the operation of the embodiment just discussed, two sweeppulses C are produced during each complete revolution or rotation ofunit [4, the first of these pulses corresponding to the duration of theinfrared scan and the second to the duration of the "visible" scan.Switch 72 is correspondingly actuated to alternately connect the signalF produced by detector 28 and'thc output of AND-circuit 62, that is,every second markingpulse E, to display tube 44 so that graphicalrepresentations F and E" of these outputs appear on screen 50. Thepulses A and B are also applied to a control grid of display tube 44 tocause suppression of the electron beam between scans.

lt WI" be appreciated from the foregoing that by varying the setting ofpotentiometer 66 the time at which an output is produced by voltagecomparator is correspondingly varied and hence the time at which markingpulse E causes actuation of pulse generator 70 during the duration ofpulse D. Thus if signal means 34 or, correspondingly, light pulsegenerator 70 emits light pulses for a predetermined orientation of unit14 the result is equivalent to directing a continuous beam of lighttoward a point in the scanning field as long as the constant angularvelocity of unit 14 exceeds a particular value.

Although the present invention has been described with reference toparticular exemplary embodiments thereof, it will be understood by thoseskilled in the art that variations and modifications may be effected inthe exemplary embodiments without departing from the scope and spirit ofthe invention.

I claim:

I. A line scanner for infrared radiation comprising, a rotatable opticalunit including a first optical system having the optical axis thereofperpendicular to the axis of rotation of said unit, a second opticalsystem having the optical axis thereof perpendicular to said axis ofrotation, deflecting means for deflecting the optical axis of said firstoptical system and the optical axis of said second optical system intocoincidence with said axis of rotation, an infrared radiation detectorresponsive to radiation received by said first optical system andoptical reference means optically connected to said second opticalsystem.

2. A line scanner as claimed in claim 1 wherein said optical axes ofsaidfirst and second optical systems are parallel.

3. A line scanner as claimed in claim 2 wherein said optical axes ofsaid first and second optical systems are colincar.

4. A line scanner as claimed in claim 1 wherein said second opticalsystem is responsive to a range of infrared radiation different fromthat to which said first optical system is responsive.

5. A line scanner as claimed in claim 1 wherein said second opticalsystem is responsive to visible light.

6. A line scanner as claimed in claim 5 wherein said optical referencemeans comprises an image-viewing system.

7. A line scanner as claimed in claim 5 wherein said optical referencemeans comprises a light pulse generator.

8. A line scanner as claimed in claim 1 further comprising a motorcoupled to said rotatable unit for driving said rotatable unit.

9. A line scanner according to claim 7 further comprising a motorcoupled to said rotatable unit for driving said rotatable unit andsynchronous control means for generating a first control pulse at apredetermined angular position of said first optical system and forgenerating a second control pulse at a predetermined angular position ofsaid second optical system.

10. A line scanner as claimed in claim 9 wherein said pulse generator isresponsive to said second control pulse.

11. Aline scanner as claimed in claim 10 further comprising means forderiving marking pulses of adjustable delay.

12. A line scanner as claimed in claim 11 further comprising an imagedisplay tube including horizontal and vertical deflection systems and ahorizontal-sweep generatorrcsponsive to said first and second controlpulses.

13. A line scanner as claimed in claim 12 further comprising switchingmeans for applying the output of said detector to said tube duringalternate horizontal sweeps and for applying marking pulses to said tubeduring the remaining alternate sweeps.

2. A line scanner as claimed in claim 1 wherein said optical axes ofsaid first and second optical systems are parallel.
 3. A line scanner asclaimed in claim 2 wherein said optical axes of said first and secondoptical systems are colinear.
 4. A line scanner as claimed in claim 1wherein said second optical system is responsive to a range of infraredradiation different from that to which said first optical system isresponsive.
 5. A line scanner as claimed in claim 1 wherein said secondoptical system is responsive to visible light.
 6. A line scanner asclaimed in claim 5 wherein said optical reference means comprises animage-viewing system.
 7. A line scanner as claimed in claim 5 whereinsaid optical reference means comprises a light pulse generator.
 8. Aline scanner as claimed in claim 1 further comprising a motor coupled tosaid rotatable unit for driving said rotatable unit.
 9. A line scanneraccording to claim 7 further comprising a motor coupled to saidrotatable unit for driving said rotatable unit and synchronous controlmeans for generating a first control pulse at a predetermined angularposition of said first optical system and for generating a secondcontrol pulse at a predetermined angular position of said second opticalsystem.
 10. A line scanner as claimed in claim 9 wherein said pulsegenerator is responsive to said second control pulse.
 11. A line scanneras claimed in claim 10 further comprising means for deriving markingpulses of adjustable delay.
 12. A line scanner as claimed in claim 11further comprising an image display tube including horizontal andvertical deflection systems and a horizontal-sweep generator responsiveto said first and second control pulses.
 13. A line scanner as claimedin claim 12 further comprising switching means for applying the outputof said detector to said tube during alternate horizontal sweeps and forapplying marking pulses to said tube during the remaining alternatesweeps.